Why is the PH of my mixed Canna Coco nutrients going up?

So, I did a search and also searched various threads, but did not see this addressed:

Background:

I grow in coco using Canna Coco nutrients. I printed the feeding schedule (light feeding) and use around 60-80% of the recommended dosage. I use 2 gallon fabric pots and mix 3 gallons of nutrients at a time in a 5 gallon Lowes bucket.

I just purchased an Apera PH60 PH meter. Previously I had gone through a number of cheap PH pens and only checked the PH once after mixing. Depending of the stage the plant(s) are in, those 3 gallons last for 3 feedings. Since I got the new, more accurate PH meter, I started checking the PH before each feeding and found the PH of the mixed nutrients keeps going up while sitting in the bucket. I add more PH down and then next feeding, the ph went up again. Usually by .5, so if I got it down to 5.5 for instance, the next day it would be 6.0.

This is true for all three feedings from the initial 3 gallon mixed nutrients.

I double checked it with my old PH meter and this is confirmed and also recalibrated my Apera PH60.

So, anyone else see this behavior?

the ph will rise as the plants take up nutrients i have found, also the smaller the amount of nutrient solution the quicker it will happen, good luck

terpedup83 said:

the ph will rise as the plants take up nutrients i have found, also the smaller the amount of nutrient solution the quicker it will happen, good luck

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While that is generally true he's talking about the mixed nutes before giving it to the plants.

Off-gassing of CO2 from your water will raise ph.

Jurassicbark said:

So, I did a search and also searched various threads, but did not see this addressed:

Background:

I grow in coco using Canna Coco nutrients. I printed the feeding schedule (light feeding) and use around 60-80% of the recommended dosage. I use 2 gallon fabric pots and mix 3 gallons of nutrients at a time in a 5 gallon Lowes bucket.

I just purchased an Apera PH60 PH meter. Previously I had gone through a number of cheap PH pens and only checked the PH once after mixing. Depending of the stage the plant(s) are in, those 3 gallons last for 3 feedings. Since I got the new, more accurate PH meter, I started checking the PH before each feeding and found the PH of the mixed nutrients keeps going up while sitting in the bucket. I add more PH down and then next feeding, the ph went up again. Usually by .5, so if I got it down to 5.5 for instance, the next day it would be 6.0.

This is true for all three feedings from the initial 3 gallon mixed nutrients.

I double checked it with my old PH meter and this is confirmed and also recalibrated my Apera PH60.

So, anyone else see this behavior?

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You neglected to mention what water you are using and if tap water it can have free ions that react fast with your pH down but have carbonates that aren't reacted right away that release more ions over time to cause the pH to go up again.

I've done the experiment in the past to make sure this isn't just a theory but an actual thing. Being a chemist who's forgotten most of it but can still figure shit out I was curious too tho I only use RO or distilled water to prevent things like this interfering with my grows.

Take a litre or a gallon, the volume doesn't really matter, of your water and pH it to what you want it for your plants. Let stand overnight or a day or more and check the pH again. If it's gone up then there's your answer. Things like carbonates will dissolve to their pH point and remain stable. Then you drop in an acid to reduce the pH which causes more to dissolve to get back to their equilibrium and the pH rises.

You could fill a container the same size you mix your nutes in then check pH once a day and add more pH down to hit target until it remains stable. Keep track of how much pH down was used to reach that point then when you you start with fresh water add your nutes first then add the amount of pH down from the experiment and the whole thing should remain stable over time unless it's something in your nutes that reacts as I described the water test. If that's the case you may want to think about using different nutes.

Many years ago I got some of the AN pH Perfect nutes and using RO water never think about pH either in DWC or pots full of ProMix HP. They make a coco version too.

Try that little experiment and see if that's it.

Also it could be that those nutes are supposed to be at the pH it keeps returning to so has buffers in it so it does that on purpose.

PJ Diaz said:

Off-gassing of CO2 from your water will raise ph.

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That's not really a thing. The tiny amount of CO2 in the water might move the needle 0.1 if at all. Reactions between the pH down and alkaline molecules in the water would produce CO2 as well.

If you're aerating then you are also replacing the CO2 with the air you are pumping in but it all isn't going to make a noticeable difference except in the lab under controlled conditions.

Very low TDS or near pure water like RO water is the way to go to avoid issues like this.

OldMedUser said:

That's not really a thing. The tiny amount of CO2 in the water might move the needle 0.1 if at all. Reactions between the pH down and alkaline molecules in the water would produce CO2 as well.

If you're aerating then you are also replacing the CO2 with the air you are pumping in but it all isn't going to make a noticeable difference except in the lab under controlled conditions.

Very low TDS or near pure water like RO water is the way to go to avoid issues like this.

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So, your assertion is that the screenshot I posed, which was written by an expert water chemist is fake news?

Jurassicbark said:

This is true for all three feedings from the initial 3 gallon mixed nutrients.

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i was gonna ask if it stabilizes after a few days but it sounds like it's used before it has a chance to. my res takes about 2 to 3 days to adjust down but then it stays stable . i mix about 20 gallons at a time with a waterfall in the res.

Best to use your well-mixed rez as soon as possible, same day, dont let it stand...just maybe mix a smaller batch more often...let the plants learn to naturally adjust the PH up for you.

PJ Diaz said:

So, your assertion is that the screenshot I posed, which was written by an expert water chemist is fake news?

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Not at all. The reactions are all correct and also support my mention of how carbonates dissolve more to raise the pH after initial treatment with pH down.

What I'm saying is that the amount of CO2 present isn't enough to cause but a minuscule change in pH and doesn't need to be part of this discussion.

Good little chart but doesn't mention that carbonic acid is very short-lived after formation.

I'm not an expert water chemist but water was involved in a great portion of my schooling to get a diploma in environmental chemistry a little over 30 years ago. Even tho CO2 levels are rising CO2 is still a very tiny amount of the air we breathe. Around 420ppm which seems a bit ironic to me.

A rising water temperature will change the PH as well, right?

OldMedUser said:

Good little chart but doesn't mention that carbonic acid is very short-lived after formation.

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I'm not a chemist, but it seems to me that's exactly what they are saying. It's short-lived as it converts to CO2 and some is offgassed.

OldMedUser said:

If you're aerating then you are also replacing the CO2 with the air you are pumping in

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But "air" is only around 4% CO2, compared to around 17% O2.

lusidghost said:

A rising water temperature will change the PH as well, right?

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Yea boiling water changes the ph level

PJ Diaz said:

I'm not a chemist, but it seems to me that's exactly what they are saying. It's short-lived as it converts to CO2 and some is offgassed.

But "air" is only around 4% CO2, compared to around 17% O2.

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420ppm is only 0.042% so you are off by two orders of magnitude. Oxygen is about 21% of our air or 210,000ppm The rest is nitrogen and tiny amounts of other gasses.

Like I said it's a tiny amount so has little impact on the pH even if it does create a little carbonic acid.

OldMedUser said:

420ppm is only 0.042% so you are off by two orders of magnitude.

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Oops, my bad. You are correct, I had errant figures.

Get a bigger res my 20 gallons stay dead on for days

OldMedUser said:

I'm not an expert water chemist but water was involved in a great portion of my schooling to get a diploma in environmental chemistry a little over 30 years ago. Even tho CO2 levels are rising CO2 is still a very tiny amount of the air we breathe. Around 420ppm which seems a bit ironic to me.

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I know that I've had issues in the past with pure water that's being aerated with an air pump/stone rising ph over time. The above theory would somewhat explain this.

As far as the OP's issue, I've experienced it as well, and I always just kind of assumed that the acids in the nute solution basically got all used up converting carbonates, which causes ph to drift back up. I'm obviously no water expert either, but I can't really find any other explanation which makes any sense.

I only use canna Terra Vega , never an issue veg up into transitions.

PJ Diaz said:

I know that I've had issues in the past with pure water that's being aerated with an air pump/stone rising ph over time. The above theory would somewhat explain this.

As far as the OP's issue, I've experienced it as well, and I always just kind of assumed that the acids in the nute solution basically got all used up converting carbonates, which causes ph to drift back up. I'm obviously no water expert either, but I can't really find any other explanation which makes any sense.

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pH should go lower if the CO2 is creating carbonic acid.

I used our hard water, 400+ppm and pH8+ to do that pH down experiment I described and once you've done it as described the carbonates will be all used up and cannot donate any more ions to react with the acid and it will stay put.

Near zero ppm RO water or distilled water are pH neutral but people still test the pH and claim it's + or - then try to pH Up or Down it anyways. pH pens can't really read the pH properly with so few free ions in so basically takes a guess. There's just nothing in it to react so one drop of acid makes it read below 7 and one drop of base will make it read above 7.

pH is a very complex subject really and if using fairly hard or even not so hard water those minerals stay behind as the plants drink the water and build up over time with repeated waterings. Just pH'ing your mix to what you want will not keep the root zone at that pH with alkaline buildup in the pots.

Now that I'm using organics with HP as my base I'll water once using our unfiltered tap water from the dugout as it has all sorts of pond bacteria and fungi in it but I also use DynoMyco as well. I seem to be getting the hang of this organics and slowly been getting better results.